US 4152608 A
The specification discloses a circuit which responds to a momentary contact closure to effect a gradual change from the "off" state to the "on" state, or a delayed change from the "on" state to the "off" state. In one embodiment, two interactive circuits are utilized to effect the above results from either of two remote locations. Each interactive circuit responds to a momentary contact closure at either location.
1. A switching system for an A-C operated device comprising:
a solid state switching device having anode and cathode main terminals and a gate terminal means for altering the impedance between said main terminals from a high impedance state to a low impedance state;
means for connecting the main terminals of said solid state switching device in series with a load and an A-C power source;
momentary contact switching means operatively connected to the A-C power source for initiating a "Turn-on" or "Turn-off" process from a quiscent "Off" and "On" state, respectively;
an accumulating capacitor operatively connected to said momentary contact switching means;
rectifying means operatively connecting said accumulating capacitor with the A-C power source for progressively increasing the charge on said accumulating capacitor following an actuation of said momentary contact switching means at a time when the system resides on an "Off" state;
discharge means connected in parallel with said accumulating capacitor for decreasing the charge on said accumulating capacitor following an actuation of said momentary contact switching means at a time when said system resides in a quiscent "On" state;
Phase shifting means connecting said accumulating capacitor to said gate terminal of said solid state switching device for varying the phase time at which the magnitude of the voltage applied to said gate terminal is sufficient to cause the impedance between said main terminals of said solid state switching device to change from a high value to a low value as an inverse function of the charge stored by said accumulating capacitor.
2. The apparatus recited in claim 1 wherein said momentary contact switching means is operatively connected to said accumulating capacitor and said discharge means by means causing the charge on said accumulating capacitor to be applied to actuate said discharge means when said momentary contact switching means is actuated at a time when the system resides in the quiscent "On" state.
3. A three-way switching system for controlling an A-C powered device from a first and second station comprising:
a first control element means at a said first station for controlling the conduction angle during a first polarity of the A-C source;
a first rectifier means at said first station for supplying half wave power to said second station during a second polarity of the A-C source;
a second control element means at said second station for controlling the conduction angle during the second polarity of the A-C source;
a second rectifier means at said second station for supplying half wave power to said first station during a first polarity of the A-C source;
circuit means at said first station for causing said first control element to change its conduction duration in response to a momentary contact closure at either of said stations and;
circuit means at said second station for causing said second control element to change its conduction duration in response to a momentary contact closure at either of said stations;.
4. The apparatus recited in claim 3 wherein said circuit means at said first station is connected to one side of the A-C power source and to one terminal of the device being controlled and comprises:
first means for detecting when the control element means at said second station is conducting and;
wherein said circuit means at said second station is connected to the other side of the A-C power source and to a second terminal of the device being controlled and comprises:
second means for detecting when the control element means at said first station is conducting.
U.S. Pat. No. 3,898,516 entitled "Lighting Control System For Incandescent Lamps" filed May 29, 1973 by Henry N. Nakasone and Application Ser. No. 595,585 now Pat. No. 4,008,416 entitled "Circuit for Producing a Gradual Change in Conduction Angle" filed July 14, 1975 by Henry H. Nakasone. The contents of each are incorporated herein by reference for the purpose of providing additional background information.
Reference is also made to a Patent Application entitled, "Soft Switch with Rapid Recovery Circuit" by Henry H. Nakasone, Ser. No. 768,547 filed concurrently herewith.
The advantages of gradual "turn-on" and delayed "turn off" have been enumerated in the above referred Patents and Patent Applications. In all prior art arrangements, however, mechanical latching switches were required in order to change the state of the circuit to increase or decrease the power applied to the load. In some applications, however, it is desirable to utilize a momentary contact switch to effect a change in the state of the circuitry. Such an arrangement is commonly utilized in household applications, for example, to achieve rapid "turn-on" and "turn-off" of lights using a wall switch which requires a very light momentary contact. Such systems typically employ special low voltage wiring between the switch and a centralized relay station. What is actually desired is a momentary contact switching system which can be used to control household lights and outlets that does not require specialized wiring and auxilliary relays. In addition, it is desirable that the power to the outlets and lights be increased gradually (to protect the loads from high current surges) and finally extinguished only after a given time delay following an initial power reduction at the time the momentary contact switch is depressed.
Accordingly, a primary object of the present invention is to provide a momentary contact light switch which can be used to replace any conventional household light switch without changing the household wiring.
Another object of the present invention is to provide a momentary contact light switch which does not utilize relays or other mechanical devices to effect a change in the state of the system.
A further object of the invention is to provide a bistable switching circuit for an A-C source which can be triggered from the "off" state to the "on" state and vice versa by depressing a momentary contact switch.
Another object of the invention is to provide a gradual change in the amount of A-C power applied to load following a change in the state of bistable switching device.
Another object of the invention is to provide a gradual "turn-on" and "turn-off" of a lamp from either of two momentary contact switches which are interconnected only by the A-C power supplied to the stations where the momentary contact switches are located.
Other objects and advantages of the present invention will be obvious from the detailed description of a preferred embodiment given herein below.
The aforementioned objects are realized by the present invention which comprises a triac, the trigger voltage of which is delayed by a phase shifting network having a phase delay dependent upon the charge of a series connected accumulating capacitor. The charge on the accumulating capacitor is in turn controlled by a transistor, the base drive of which is changed by momentary depression of a switch which (1) either "cuts-off" the transistor by partially discharging a base holding capacitor through the accumulating capacitor or (2) causes the transistor to conduct by transferring a portion of the accumulating capacitor charge to the base holding capacitor where control from either of two remote locations is desired. The individual switch circuits are adopted to include a current sensing transistor. The actuation of a momentary contact switch at one station is sensed by the voltage developed across the base emitter junction of the current sensing transistor at the other station. As a consequence, both circuits are activated from the "off" state to the "on" state and vice versa by momentary closure of contacts at either location. The rate at which the "turn-on" or "turn-off" proceeds can be changed from instantaneous (not observable to human beings) to several seconds (depending upon the values of the components.
FIG. 1 shows a schematic diagram of a preferred embodiment of the invention for use at a single station.
FIG. 2 shows a convention three-way wiring arrangement in the "off" state.
FIG. 3 shows a schematic diagram of a preferred 3-way switch embodiment for use in an existing household wiring arrangement.
Adverting to the drawings, and particularly FIG. 1, a preferred embodiment of the invention comprises a triac 1 having an integral diac 2, a firing capacitor 3, a phase shifting network comprising capacitor 4 and diodes 5 and 6, the delay of which is dependent upon the charge of an accumulating capacitor 7. Switch 8 is a momentary contact push button, which in most applications will be wall mounted in a manner similar to convention household light switches. The base holding capacitor 9 functions to store a positive charge for maintaining transistor 10 in the "on" (conducting state) so that triac 1 will remain off until switch 8 is depressed. Capacitor 11 functions to produce a slight (2 second) delay in turning transistor 10 "on" when switch 8 is depressed to turn the circuit "off." The operation of the circuit is described below.
As an initial condition, it will be assumed that Triac 1 is non-conducting so that the full A-C voltage appears across points 20 and 21. Capacitor 9 will thus be charged to a positive potential, and transistor 10 will be turned "on" by virtue of the base current flowing through zener diode 19. The current flowing in the collector of transistor 10 maintains capacitor 7 discharged so that (with the value of capacitor 4 and resistor 22 chosen sufficiently large) the voltage swing at junction 22 is insufficient to breakdown diac 2. In essence, the feedback through neon 17 diode 23, resistor 24, and zener 19 is positive, and the circuit remains in its quiescent "off" state until something changes.
When switch 8 is depressed, current flows through resistor 25 causing the charge on capacitor 9 to decrease and the charge on capacitor 7 to increase. As a consequence, transistor 10 stops conducting and triac 1 begins to conduct during the latter part of each A-C half cycle. Capacitor 7 continues to charge by virtue of the current flowing in resistor 22, phase shifting capacitor 4 and diode 15 so that triac 1 fires progressively earlier each half cycle. When the conduction angle increases to a degree such that the voltage across points 20 and 21 is less than that required to breakdown neon 17, recharge of capacitor 9 is precluded (it will be understood that the component values are chosen so that this occurs prior to the time that capacitor 9 is recharged to a voltage equal to that of zener 19). The circuit thus continues with the gradual turn "on" process until the quiescent "on" state is achieved (i.e., capacitor 7 fully charged to a value equal to twice that of the breakdown voltage of diac 2 and triac 1 conducting for approximately 90% of the input cycle).
After the "on" state is reached, switch 8 can be momentarily depressed to initiate the delayed "turn-off" process. When this occurs, a portion of the charge on capacitor 7 is transferred to capacitor 9 through resistor 25, so that both capacitors assume the same voltage. (The values of the components are chosen such that this voltage will be in excess of the breakover voltage of Zener 19). Transistor 10 thus begins to conduct and the decreased potential on capacitor 7 reduces the conduction angle to a point such that neon 17 fires to maintain the charge on capacitor 9. The circuit thus proceeds to "turn-off" within a time span which is determined by the values of the components 24, 26 and 7.
In summary, the circuit has two stable states (quiscent "off" and quiscent "on" and two unstable states (gradual "turn-on" and gradual "turn-off"). The duration of the latter can be long (3 to 8 seconds) or imperceptably short (0.1 to 0.5 seconds) to the observer, depending upon the desired effect.
While the circuit of FIG. 1 is totally satisfactory for controlling a light or other apparatus from a single location, it cannot be used in a standard three-way configuration like that shown in FIG. 2 unless additional wires are added. What is desired, therefore, is a momentary contact switching arrangement for achieving gradual "turn-on" and delayed "turn-off" from either of two remote locations utilizing the existing A-C house wiring N, M, R1 and R2. This objective is realized by the circuit shown in FIG. 3.
In FIG. 3 an operator can effect gradual "turn-on" or delayed "turn-off" from either of two locations. The circuits at station one and two of FIG. 3 are identical, the components such as SCR T11 at station one corresponding to an identical counterpart T12 at station two, capacitor C11 at station one corresponding to C12 at station two, and so forth. The circuit at station one is connected to one side of the A-C line M at A1 and to one side of the lamp 10 wire R1 at J1. The circuit at station two is connected to the other side of the A-C line N at A2 and to the opposite side of the lamp 10 wire R2 at J2. An explanation of the interactive operation of the two circuits will be described in terms of the following sequence of events:
1. Off State
As an initial condition, it will be assumed that the voltage on accumulating capacitors C31 and C32 is zero so that neither SCR T11 or T12 will conduct during any part of the cycle. It will also be assumed that Q21 is "Off" so that Q11 is biased "On" by virtue of the current flowing through D42, R92, D81, R61, D61 and Zener diode Z11 whenever the "N" side of A-C source is positive with respect to the "M" side. Similarly, it will be assumed that Q22 is "Off" so that Q12 is biased "On" by virtue of the current flowing through D41, R91 D82, R62, D62 and Zener diode Z12 whenever the "M" side of the A-C source is positive with respect to the "N" side.
In addition to these currents (which are limited to a small fraction of a milliamp by the value of resistors R61 and R62) small additional currents flow through R11 and R10 which would charge capacitors C31 and C32 were it not for the current flowing in the collectors of Q11 and Q12 respectively. It will be noted also that during the "Off" state capacitors C51 and C41 charge to a voltage which is approximately equal to the breakdown voltage of Z11 (typically 25 volts) whereas C42 and C52 charge to voltage equal to the breakdown voltage of Z12 (also typically 25 volts).
2. Gradual "Turn-on"
"Turn On" is effected by depressing either of the momentary contact switches S11 (at station one) or S12 (at station two). Since the circuits are identical, the interactive relationship will be described by assuming that switch S11 is depressed. When this occurs the capacitors C51 and C41 (which have been charged to the breakdown voltage of Z11 during the quiescent "Off" state) discharge through R51 and R81 to raise the voltage of C31 to effect a decrease in the phase delay of capacitor C21. As a consequence, SCR T11 begins to conduct near the end of the next positive half cycle (i.e., line N positive with respect to line M). The discharge of capacitors C51 and C41 cuts off base current to Q11 enabling the charge on C31 to increase during each positive half cycle--thus progressively increasing the conduction angle of T11. The conduction of SCR T11 also causes Q22 at station two to turn "On" as a consequence of the voltage developed across D42 and R92 (the latter having a low ohmic value (e.g., 100Ω) to prevent turn "On" of Q22 (as a consequence of the minute currents drawn by R61 and R11 in the "Off" state (prior to the time T11 conducts). When Q22 conducts, C52 is discharged, thus cutting off drive current to the base of Q12 allowing C32 to charge during each negative half cycle (line "M" positive with respect to line "N"). As the voltage of C32 increases, a point is reached where SCR T12 begins to conduct. Thereafter the charge on C32 increases with each positive half cycle ("M" positive with respect to "N") with a resultant increase in conduction angle.
Were it not for the conduction of T12, the capacitor C41 would be recharged through D51, thus causing Q11 to conduct to return the system to the "Off" state. It will be noted, however, that the conduction of SCR T12 at station two causes Q21 to conduct in exactly the same manner that the conduction of SCR T11 caused Q22 to conduct. Hence, C51 will be discharged during each half cycle in which T12 conducts causing Q11 to remain "Off."
In summary, depression of either S11 or S12 will cause the associated SCR (T11 or T12) to commence conducting. The conduction angle increases in accordance with the rate at which the associated accumulating capacitor (C31 or C32) charges. Conduction of an SCR at one station also causes the current sensing transistor (either Q22 or Q21) at the opposite station to conduct so as to cut off the associated accumulating capacitor discharge transistor (either Q12 or Q11) allowing the SCR at the opposite station to commence conducting. The gradual turn "On" process continues with both SCRs conducting for progressively greater durations until the quiescent "On" state is reached.
3. Delayed Turn Off
After the quiescent "On" state is reached, capacitors C31 and C32 will be charged to a voltage which is approximately twice that of the breakdown voltage of the associated diac (either B11 or B12). Typically, this will be in the range of 50 volts. Depression of either S11 or S12 will cause the charge so stored to be abruptly transferred to the base holding capacitor (either C41 or C42) which immediately causes the associated accumulating capacitor discharge transistor (either Q11 or Q12) to conduct. Thus if C31 is chosen as 10 μf and is charged to 50 volts and C41 is 5 μf, closure of S11 will discharge C31 through R51 until the voltage on C41 and C31 are equal. If C41 maintains a charge of 20 volts during the off state (by virtue of the charge and discharge of C51 through R61 and Q.sub. 21) then the voltage on C41 will rise to approximately 40 volts upon closure of S11 causing Q11 to rapidly discharge C31, completely cutting off conduction of SCR T11 until the voltage of C41 has dropped to a point such that the Q11 collector current is insufficient to maintain C31 discharged. If R41 is chosen as 1.5 megohms, this duration is approximately 5 seconds--it is thus necessary to cut off Q21 to recharge C41 within this time period.
It will be noted that Q22 ceases to conduct when T11 is cut off. As a consequence, C42 begins to charge through D82, R62, and D52. If R61 is chosen so that the time required to activate Q12 is less than 5 seconds, then C32 will be discharged so as to cut off T12 (and consequently Q21) within the critical 5 second period to prevent a spurious reactivation of the system to the "On" state.
In summary, momentary depression of S11 discharges the associated accumulating capacitor C31 and charges the associated base holding capacitor C41 which supplies base current to the associated accumulating capacitor discharge transistor Q11. The latter functions to complete and maintain C31 discharged, thus cutting off T11 and Q22 for a time greater than that necessary to cut off T12 by charging C42 through R62. Since both circuits are identical, the same result is achieved (in reverse order) by momentarily depressing S12 instead of S11 --either switch functioning to abruptly decrease the light intensity by 1/2 for several seconds followed by complete extinguishment.
Values of Components:
Resistors R11 and R12 should be chosen in conjunction with capacitors C21 and C22 respectively so as to assure that the potential applied to diacs B11 and B12 does not exceed their breakdown voltage when capacitors C31 and C32 are fully discharged. Capacitors C11 and C12 should be chosen as small as possible--consistant with reliable triggering of the SCR's T11 and T12. Resistors R91 and R92 should be chosen to adequately discharge C11 +C21 and C21 +C22 during the "Off" state to prevent a spurious firing of the SCR's due to a charge "build-up" across the diacs B11 and B12. Capacitors C31 and C32 should be approximately twice the value of C41 and C42, the actual value being dependent upon the desired "turn-on" time and "turn-off" delay. Zeners Z11 and Z12 should be about 20- 25 volts. Capacitors C61 and C62 should be chosen in conjunction with resistor R41 and R42 to provide a slight delay (0.5 to 1 seconds). This prevents discharge of C41 or C42 by delaying "turn-on" of Q11 or Q12 if S11 or S12 is not released immediately when initiating the delayed "turn-off" process. Resistors R51 and R52 should provide a time delay of approximately 0.1 seconds in equalizing the voltage between capacitors C41 -C31 and C42 -C32. Resistors R61 and R62 should be chosen in conjunction with capacitors C51 and C52 so that the latter will charge to approximately 20 volts during 1/2 cycle of the A-C. Resistors R91 and R92 should be chosen to prevent "turn-on" of their respective transistors (Q21 and Q22) due to the minor currents flowing when the system is in the quiscent off state. Resistors R71 and R72 should be small enough to adequately discharge C51 during 1/2 cycle of the A-C input.
The present invention accomplishes results not possible with any prior art switching arrangements. Although the teachings have been described in conjunction with particular circuits, it will be understood that the basic concepts of the invention are not limited thereto, and that numerous changes, modifications and substitutions may be made without departing from the spirit of the invention.